1. Field of the Invention
The present invention relates to a method of assembling a carriage assembly for use in a magnetic disk apparatus where suspensions are attached to front end portions of carriage arms, and to an assembling apparatus that uses such method.
2. Related Art
FIG. 5 is a view showing the external appearance of a carriage assembly used in a magnetic disk apparatus. In FIG. 5, reference numeral 10 designates carriage arms and 12 one example of a suspension that is connected to front ends of the carriage arms 10. A magnetic head 14 is mounted on a front end portion of each suspension 12. Each magnetic head 14 is electrically connected via a flexible circuit board 16, which is attached to side surfaces of the carriage arms 10, to a control unit 18. Reference numeral 19 designates an actuator shaft that is fixed to a base portion of the carriage arms 10. The carriage arms 10 rotate about the axis of the actuator shaft 19 to carry out seek operations on flat planes that are parallel to the surfaces of recording media.
The carriage assembly is formed by fixing each suspension 12 by crimping to both surfaces of a front end portion of one out of the carriage arms 10 that are attached so as to be parallel to the actuator shaft 19.
A conventional method of fixing the suspensions 12 to the carriage arms 10 is disclosed by Patent Document 1. FIG. 7 shows the conventional method of fixing the suspensions 12 to the carriage arms 10 disclosed in Patent Document 1.
According to this conventional method, after the suspensions 12 have been aligned with and placed upon the front ends of the respective carriage arms 10, a metal ball 20 formed with a slightly larger diameter than an inner diameter of spacer holes 12b provided in the suspensions 12 is passed through the spacer holes 12b to fix the suspensions 12 to the carriage arms 10 by crimping. Reference numeral 22 designates a pressing shaft for pressing the metal ball 20 to cause the metal ball 20 to pass through the spacer holes 12b. 
FIG. 6 shows an operation that passes the metal ball 20 through the spacer holes 12b of the suspensions 12 to fix the suspensions 12 to the carriage arms 10 by crimping. The suspensions 12 are placed on both surfaces of the respective carriage arms 10 with the fitting holes 10a and the spacer holes 12b in alignment. Since the metal ball 20 is formed with a slightly larger diameter than the spacer holes 12b, when the metal ball 20 is passed through the spacer holes 12b, the metal ball 20 acts so as to press open crimping portions 13 formed on inner circumferential edges of the spacer holes 12b, and as a result, the suspensions 12 are fixed so as to “bite into” the carriage arms 10. As shown in FIG. 6, during a single crimping operation, the metal ball 20 is caused by the pressing shaft 22 to strike one carriage arm 10 after another and therefore moves successively through the spacer holes 12b. 
In this way, when assembling a carriage assembly, conventionally the metal ball 20 is used to press open the spacer holes 12b to fix the suspensions 12 to the carriage arms 10 by crimping. Accordingly, depending on the balance between the external diameter of the metal ball 20 and the internal diameter of the spacer holes 12b, a problem can occur where the spacer portions 12a deform due to stress that acts thereupon during crimping, resulting in the suspensions 12 becoming displaced from the standard positions. That is, when the suspensions 12 are fixed to the carriage arms 10 by crimping, the spacer portions 12a become bent, which can result in the suspensions 12 becoming tilted with respect to the standard angle. Tilting of the suspensions 12 affects the float heights of the magnetic heads 14 above the surfaces of the recording media resulting in fluctuation in the float heights of the magnetic heads 14 above the surfaces of the recording media.
The storage capacity of modern magnetic disk apparatuses has been greatly increased, which has led to the float height of magnetic heads above the surfaces of recording media being kept low. This means that fluctuations in the float height of magnetic heads have a large effect on the information reading and writing characteristics, and therefore there are demands for the suppression of fluctuation in the float height of the magnetic heads to produce the required characteristics.
Patent Document 1 discloses a method of assembling a carriage assembly that can suppress deformation of the spacer portions 12a due to the stress applied during crimping. FIG. 8 is a diagram useful in explaining a method of assembling a carriage assembly using an ultrasonic horn 32 disclosed in Patent Document 1 as a method of assembling that can suppress deformation.
The method of assembling a carriage assembly disclosed in Patent Document 1 is characterized by using the ultrasonic horn 32 to pass the metal ball 20 through the spacer holes 12b. The metal ball 20 is the same as the metal ball 20 used in the method of assembling a carriage assembly described above. FIG. 8 shows a state of an assembly where gap maintaining plates 36 are inserted between adjacent carriage arms 10 and pressure applying plates 37a, 37b are placed in contact with both end surfaces of the carriage arms 10 so that the respective carriage arms 10 are supported by being sandwiched on both sides thereof.
The ultrasonic horn 32 applies ultrasonic vibration in the axial direction and due to the action of the ultrasonic horn 32, the metal ball 20 causes less damage to the spacer portions 12a during crimping, so that deformation is prevented when the suspensions 12 are attached to the carriage arms 10 and the suspensions 12 can be fixed to the carriage arms 10 more accurately. The reason for this is thought to be that the stress caused by the ultrasonic vibration of the ultrasonic horn 32 and the static stress due to the metal ball 20 pressing open the crimping portions 13 act so as to be superimposed, which makes it possible to reduce the resistance to deformation, and by reducing the average machining force by using a striking action that is repeated at high speed, it is possible to fix the members while suppressing deformation of the fixed portions of the suspensions 12 and the carriage arms 10.
Patent Document 1
Japanese Laid-Open Patent Publication No. 2004-127491 (see paragraphs 0003, 0004, 0015, 0023, and 0024 and FIGS. 3, 5, and 6).
However, with the above conventional method of assembling a carriage assembly that uses ultrasonic vibration, there is the problem of large fluctuations in the crimped (deformed) state of the spacer portions, that is, the spacer portions are too greatly or conversely insufficiently crimped (deformed).
When the crimping is too strong, that is, when a spacer portion is too greatly deformed, there is the problem of the spacer portion becoming bent, which causes the suspension to become tilted from the standard angle. Conversely, when the crimping is too weak, the suspension is not stably fixed to the carriage arm, resulting in problems such as rattling.